1. Field of the Invention
The invention relates in general to a memory cell and a manufacturing method thereof, and more particularly to a one-transistor dynamic random access memory cell and a manufacturing method thereof.
2. Description of the Related Art
Recently, dynamic random access memories (DRAM) are widely applied to personal computers and all kinds of accessories, such as graphic cards, scanners, printers, fax machines and video compression cards. In addition to the conventional dynamic random access memory (1T1C-DRAM) including a transistor and a capacitor, a one-transistor dynamic random access memory (1T-DRAM) is developed recently. A floating body is used for storing carriers in order to store data. By simplifying the structure of the memory, the storage density per unit area is increased, and the manufacturing process is simplified as well. Furthermore, because the one-transistor dynamic random access memory reads data in a non-destructive way, the service life of the memory is prolonged. Therefore, the one-transistor dynamic random access memory has great potential and becomes one of the most important research directions nowadays.
Generally speaking, memory cells are formed on a silicon-on-insulator wafer (SOI wafer) in the one-transistor dynamic random access memory for separating the floating body in a semiconductor layer among a source region, a drain region, a bottom oxide layer and a gate oxide layer to store the carriers. However, as the manufacturing process of the memories progresses, the size of the memory device becomes smaller. The length of the channel between the source region and the drain region in the cell is shortened. When the length of the channel is shortened to a certain level, short channel effects, like low threshold voltage, punch through effect and drain induced barrier lowering (DIBL), can occur. As a result, the stability of memory operation is affected seriously. Moreover, because the carriers leak out from the junctions between the semiconductor layer, the drain and the source, the retention time of the carrier can not be increased. Therefore, the product quality can not be further improved.